The present invention described herein relates to the field of seats for ejecting aviators from aircraft. More specifically, the invention relates to fins deployed on an ejection seat to stabilize the seat with respect to yaw. The invention especially relates to an apparatus for deploying a yaw stabilizing fin for an ejection seat.
An aircraft advanced ejection seat can be equipped with a fin (or fins) that stabilizes against yaw when the seat is ejected and falls through the air. As long as the seat remains in the aircraft, the yaw stabilizing fin need not be deployed or oriented into its yaw stabilizing orientation. Often the fin is folded about a pivot and stowed against the sides of the ejection seat. However, when the seat is ejected, the yaw stabilizing fin is automatically deployed.
The stabilizing yaw fin is generally deployed through a 90 degree angle with respect to the back of the ejection seat. A known apparatus for yaw stabilizing fin deployment has one end of a lanyard connected to the tip of the fin by an open face hook. The other end of the lanyard is attached to the aircraft. The fin is retained in its folded or stowed position by a shear pin rated for a specific shear force, for example, 200 lb.. When the ejection seat is ejected, the lanyard is made taut by the ejection seat's pulling on the lanyard in a direction away from the aircraft, thereby providing a deploying force to a hook at the tip of the fin. To overcome the rating of the shear pin when the fin is deployed, at least 200 lb. of force is applied to the lanyard and initiates deployment of the fin. However, due to the fact that the hook on the fin has an open face, once the fin is oriented at an approximate 15 degree angle with respect to the back of the ejection seat, the lanyard slips off the hook. Since the fin must continue to rotate to 90 degrees to become fully operational, the fin must travel the remaining 75 degrees utilizing the momentum created by the lanyard in the first 15 degrees of deployment.
The fin begins to lose momentum and decelerate as soon as the deploying lanyard slips off the hook, and the fin continues to experience deceleration during deployment from 15 to 90 degrees. Such a fin is subject to deployment failure in instances where the fin experiences a high acceleration load in the direction opposite to that of deployment. It would be desirable to provide a fin deployment mechanism that does not depend upon momemtum experienced by the fin during partial deployment to complete the full deployment of the fin.
The connection of the lanyard to the fin at the fin tip has a disadvantage. High aerodynamic loads can bring about a large frictional force at the fin pivot point and thereby retard or prevent proper deployment of the fin. Therefore, it would be desirable to provide a fin deployment mechanism that does not undergo large frictional forces at a fin pivot point which retard or prevent proper deployment of the fin.
Another problem associated with the known fin deployment mechanism is that only one spring loaded locking pin is provided and is actuated when the fin deploys the full 90 degrees. However, if the fin does not deploy the full 90 degrees, then it could fall back to the stowed position rendering the fin useless as a yaw stabilizing control surface. It would be desirable, therefore, to provide a fin deployment mechanism that prevents a fin from falling back to the stowed position in a case where the fin is only partially deployed.
Other deployment mechanisms for ejection seat stabilizing fins are disclosed in the U.S. Patents. U.S. Pat. Nos. 3,027,124 and 3,662,978 disclose fins deployed by hydraulic cylinders. Hydraulic cylinders are complex and weighty structures, and it would be desirable to provide a fin deployment mechanism that does not utilize hydraulic cylinders.
U.S. Pat. No. 4,470,565 discloses fins deployed by torsion springs located at the pivot points of the fin to the seat. Considering the fact that a large amount of momentum is generated when an ejection seat is ejected from an aircraft, it would be desirable to provide a fin deployment mechanism that utilizes the momentum of an ejected seat without requiring springs to bring about deployment.
U.S. Pat. No. 4,480,806 discloses a stabilizing fin deployed by the force of a moving airstream acting upon the fin. A problem with depending upon a moving airstream for deployment is that an airstream is inconsistent and unreliable. U.S. Pat. No. 4,462,562 discloses deployment of a stabilizing bellows-like afterbody, not a fin, upon ejection of the seat. The folded bellows is unfolded by a lanyard that becomes taut when the seat is ejected from the aircraft.
A common problem present with the known yaw stabilizing fin deployment mechanisms is that none of the known fin deployment devices provides a simple and reliable deployment mechanism that provides a continuous force during the entire range of fin deployment.
Another common problem present with the known yaw stabilizing fin deployment mechanisms is that they lack a locking mechanism that locks a partially deployed fin and prevents a partially deployed fin from returning to the stowed position.